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Aug. 19, 2011 -- Women who take a multivitamin every day around the time of conception appear to have a reduced risk for delivering low-birth-weight babies, a new study shows.

Daily multivitamin use was also associated with a lower preterm birth risk among normal-weight, but not overweight, women.

Since about half of pregnancies are unplanned, taking a multivitamin every day could prove to be an important intervention for improving birth outcomes, especially among women who are not actively trying to conceive a child, study leader Janet M. Catov, PhD, of the University of Pittsburgh, tells WebMD.

“Just like folic acid supplementation, multivitamin use immediately before and after conception may be a simple strategy for lowering pregnancy risk,” she says.

Vitamins and Birth Risk

In earlier research, Catov and colleagues found that taking a multivitamin in the months before and after conception decreased the risk for developing the pregnancy-related condition preeclampsia, which can lead to stroke and even death.

That study and the newly published one included close to 36,000 Danish women enrolled in a national birth registry who were asked about their use of multivitamins in the weeks before and after conception.

About 60% of the women reported taking multivitamins during this period.

After adjusting for risk factors for preterm birth -- including smoking, obesity, and age -- normal-weight and underweight women who took multivitamins had a 16% reduction in preterm delivery risk compared to women who did not take the supplements.

Catov says it is not clear why a similar association was not seen in overweight women.

Multivitamin use in the weeks before conception was associated with a 10% to 20% reduction in low birth weight, regardless of the weight of the mother-to-be. Taking multivitamins regularly in the weeks after conception was associated with a 33% reduction in risk.

The study, which appears online today, will be published in the September issue of the American Journal of Clinical Nutrition.

More Than Just Folic Acid

The benefits of taking the vitamin-B supplement folic acid around the time of conception and eating folate-rich foods are well established. The vitamin is known to reduce the risk for preterm births, low birth weight, and neural tube birth defects.

Most multivitamins contain folic acid, but the researcher says other nutrients in the vitamins -- including zinc, and vitamins C and E -- may also contribute to better birth outcomes.

No evidence of harm associated with multivitamin use was seen in the study, but Catov says the researchers will continue to study this.

“We need to look more closely at the potential for adverse outcomes before recommending multivitamin use as a strategy for lowering pregnancy risk,” she says.

Ob-gyn Jennifer Wu, MD, of Lenox Hill Hospital in New York City, already recommends multivitamins that contain calcium to her patients when they tell her they are trying to conceive.

“Taking a multivitamin is a good habit to get into because many women have nutritional deficiencies that we want to correct, ideally before conception,” she tells WebMD. “It is not just about pregnancy. Many younger women don’t get enough calcium and these women are missing out on bone building that will help protect them in their 60s and 70s.”